1. Field of the Invention
The present invention relates to a structure of a vibration wave motor driven by a travelling vibration wave.
2. Description of the Prior Art
As disclosed in U.S. Pat. No. 4,019,073, a vibration wave motor transduces a vibration caused by an application of a periodic voltage to an electro-strain element to a rotational motion or a one-dimensional motion. Since it does not require any winding unlike a conventional electric motor, it is simple in structure and compact, provides a high torque at a low rotating speed and has a small inertial rotation.
However, the prior art vibration wave motor friction drives a movable member such as a rotor which contacts to a vibrating member to transduce a standing wave vibration created in the vibrating member to a unidirectional motion of the moving member.
In order to reverse the direction of motion, it is necessary to change a mechanical structure such as to change a contact position and/or a contact angle of the vibrating member and the moving member. Accordingly, a large scale device is needed to attain the reversible vibration wave motor and the advantages of the vibration motor, that is, the simple structure and the compactness are lost.
In order to resolve the above problem, a vibration wave motor driven by a travelling vibration wave has been recently proposed.
FIG. 1 shows a structure of such a vibration wave motor, in a disassembled state.
A vibration absorber 4, a metal ring vibrating member 2 having electro-strain elements 3 mounted on a side facing the absorber 4 and a moving member 1 are inserted, in this order, in a central cylinder 5a of a stator 5 serving as a base. The stator 5, the absorber 4, the electro-strain elements 3 and the vibrating member 2 are mounted in a manner not to rotate relative to each other. The moving member 1 is press-contacted to the vibrating member 2 by its gravity or urging means, not shown, in order to keep an integrity of the motor.
A plurality of electro-strain elements 3a are arranged at a pitch of one-half of a wavelength .lambda. of the vibration wave, and a plurality of electro-strain elements 3b are also arranged at the pitch of .lambda./2. Instead of the plurality of electro-strain element 3a (or 3b), a single element polarized at the pitch of .lambda./2 may be used. The electro-strain elements 3a and 3b are arranged phase-differentially to each other such that the pitches are staggered by (n.sub.0 +1/4).lambda., where n.sub.0 =0, 1, 2, 3, . . . . Lead wires 11aare connected to the electro-strain elements 3a and lead wires 11b are connected to the electro-strain elements 3b. They are connected to an A.C. power supply 6a and a 90.degree. phase shifter 6b (see FIG. 2). A lead wire 11c is connected to the metal vibrating member 2 and it is connected to the A.C. power supply 6a.
A friction area 1a of the moving member 1 is made of a hard rubber to offer a high friction force and reduce abrasion and it is press-contacted to the vibrating member 2.
FIG. 2 shows generation of the vibration wave in the motor. While the electro-strain elements 3a and 3b attached to the metal vibrating member 2 are shown adjacent to each other for the sake of convenience of explanation, they meet the requirement of .lambda./4 phase shift described above and are essentially equivalent to the arrangement of the electro-strain elements 3a and 3b of the motor shown in FIG. 1. Symbols .sym. shown in the electro-strain elements 3a and 3b indicate that they expand in a positive cycle of the A.C. voltage, and symbols .crclbar. indicate that they shrink in the positive cycle of the A.C. voltage.
The metal vibrating element 2 is used as an electrode for the electro-strain elements 3a and 3b, and an A.C. voltage of V=V.sub.0 sin .omega.t is applied to the electro-strain elements 3a from the A.C. power supply 6a and an A.C. voltage of V=V.sub.0 (.omega.t.+-..pi./2) which is .lambda./4 phase shifted by the 90.degree. phase shifter 6b is applied to the electro-strain elements 3b from the A.C. power supply 6a. The sign + or - in the equation is selected by the phase shifter 6b depending on the direction of movement of the moving member 1 (not shown in FIG. 2). When the + sign is selected, the phase is shifted by +90.degree. and the moving member 1 is moved in a forward direction, and when the - sign is selected, the phase is shifted by -90.degree. and the moving member 1 is moved in the reverse direction.
Let us assume that the - sign is selected and the voltage of V=V.sub.0 sin (.omega.t-.pi./2) is applied to the electro-strain elements 3b . When only the electro-strain elements 3a are vibrated by the voltage of V=V.sub.0 sin .omega.t, a standing wave vibration is generated as shown in FIG. 2(a), and when only the electro-strain elements 3bare vibrated by the voltage of V=V.sub.0 sin (.omega.t-.pi./2), a standing wave vibration as shown in FIG. 2(b) is generated.
When the two A.C. voltages having the phase shift therebetween are simultaneously applied to the electro-strain elements 3a and 3b, respectively, the vibration wave travels. FIG. 2(c) shows a wave at time t=2n.pi./.omega., FIG. 2(d) shows a wave at time t=.pi./2.omega.+2n.pi./.omega., FIG. 2(e) shows a wave at time t=.pi./.omega.+2n.pi./.omega. and FIG. 2(f) shows a wave at time t=2.pi./2.omega.+2n.pi./.omega.. As seen, a wave front of the vibration wave travels in an x-direction.
Such a travelling vibration wave has a longitudinal wave and a transverse wave. Looking at a mass point A of the vibrating member 2 shown in FIG. 3, it makes a counterclockwise rotating elliptic motion by a longitudinal amplitude u and a transverse amplitude w. The moving member 1 is press-contacted (arrow p) to the surface of the vibrating member 2 and it contacts only to an apex of the vibrating plane. It is therefore driven by elliptic components of the longitudinal amplitude of the elliptic motions at mass points A, A', . . . at the apexes that it is moved in a direction of an arrow N.
A velocity of the mass point A at the apex is V=2.pi.fu (where f is a frequency). A velocity of movement of the moving member 1 depends on it and also depends on the transverse amplitude w because of the friction drive by the press-contact. Thus, the velocity of movement of the moving member 1 is proportional to the magnitude of the elliptic motion of the mass point A and the magnitude of the elliptic motion is proportional to the voltage applied to the electro-strain elements.
However, since the metal elastic vibrating member 2 is used as the common electrode to the electro-strain elements 3a and 3b in the prior art vibration wave motor as described above, the A.C. voltage source or the positive and negative voltage sources for generating the A.C. voltage are required as the driving power source.
In such a vibration motor, the lead wires for supplying the voltage to the electro-strain elements are soldered directly to the electro-strain elements. Accordingly, it is not adapted to mass production, the solders are apt to be torn off by the vibration, the vibration frequency varies depending on the quantity of the solders, and the electro-strain elements are deteriorated by the heat of soldering.